The light control glass containing a light control suspension is a glass invented unprecedentedly by Edwin Land (U.S. Pat. Nos. 1,955,923 and 1,963,496 specifications), and the form thereof has a structure wherein a light control suspension in a liquid state is injected into a narrow gap between two transparent electroconductive substrates. According to the invention by Edwin Land, in the liquid light control suspension injected into the gap between the two transparent electroconductive substrates, most of incident light is reflected, scattered or absorbed on or into light control particles dispersed in the suspension by Brownian motion of the light control particles when no electric field is applied to the suspension. Thus, only a very slight portion thereof is transmitted therethrough.
In other words, the degree of the transmission, the reflection, the scattering or the absorption is decided in accordance with the shape, the nature and the concentration of the light control particles dispersed in the light control suspension, and also in accordance with the amount of light energy radiated thereto. When an electric field is applied to a light control window made of a light control glass having the above-mentioned structure, an electric field is formed in the light control suspension through the transparent electroconductive substrates so that the light control particles exhibiting a light control function are polarized to be arranged in parallel to the electric field. As a result, light is transmitted between the light control particles. Finally, the light control glass turns transparent.
However, such an early light control device has not been easily put into practical use because of the aggregation of light control particles in the light control suspension, the sedimentation by their own weight, a change in the color tone by heat, a change in the optical density, a deterioration caused by the radiation of ultraviolet rays, difficulty in a maintenance of the gap between the substrates and in the injection of the light control suspension into the gap, and the like.
The specifications of U.S. Pat. Nos. 3,756,700, 4,247,175, 4,273,422, 4,407,565 and 4,422,963 issued by Robert. L. Saxe, the specification of U.S. Pat. No. 3,912,365 issued by F. C. Lowell or that of U.S. Pat. No. 4,078,856 issued by R. I. Thompson discloses a light control window using a light control glass complementing initial problems of a light control window, that is, the aggregation and the sedimentation of light control particles, a change in the optical density, and others.
According to these patents and so on, by effect of a liquid-state light control suspension composed of a needle-form light control crystal particles, a suspending agent for dispersing the crystal particles, a dispersion adjustor, a stabilizer and others, the density of the light control particles and that of the suspending agent are made substantially equal to each other to prevent the sedimentation of the light control particles. In addition thereto, the addition of the dispersion adjustor makes the dispersibility of the light control particles high, thereby preventing the aggregation of the light control particles to solve the initial problems.
However, these light control glasses each have a structure wherein a liquid light control suspension is enclosed in a gap between two transparent electroconductive substrates, as seen in conventional light control glasses. Thus, when a large-sized product is produced, it is difficult to enclose a suspension uniformly into the gap between two transparent electroconductive substrates, and a swelling phenomenon is easily caused at the lower region of the product by a hydraulic pressure difference between the upper and lower regions of the product. Moreover, the optical density is varied by a change in the interval between the substrates, which is caused by external environments, for example, the pressure of wind, so that the color tone is easily turned heterogeneous. Furthermore, a surrounding sealing member for storing the liquid between the transparent electroconductive substrates is broken so that the light control material leaks or other problems are caused. Additionally, the response time becomes uneven by a deterioration caused by ultraviolet rays, or a voltage drop between the periphery of the transparent electroconductive substrates and the center.